Please Help

A multiple stories Yaoi manga. I Only remember the story about a boy who was being helped by an old man after the boy get into a fight. Before the fight the boy had a female friend, but she betrayed him. And for I can remember the boy was selling his body because he musts get food to live on, and food is hard to get because the earth is no longer friendly. After being helped by the old man the boy interested in him and they are having sex right before a world's end {doomsday(?)}